Building Design

A number of factors other than the building materials from which it is made, determine the degree to which a building is green. The shade of the green label which can be assigned to a building reflects its sustainability over a long lifespan with low energy inputs. It is dependent upon the location of the building in relation to its accessibility, the geometry of the building envelope, the relation of the building to its site, and also on the ways in which the users and the builders themselves are affected by the building.

Access to buildings will be dealt with more thoroughly in Chapter 3, in which transportation in the city is examined. It is sufficient to point out here that the 'green building' set in a park on the periphery of a city served only by roads used entirely by the private motor car is a contradiction in terms. Any energy savings made by the greening of the building would be lost during the building's lifetime through the expenditure of energy in maintaining the essential links with the users. The first requirement of the green building - however pale the shade of green - is a satisfactory location; that is, it should be in close proximity to the public transport system and sited within walking and cycling distance of important connected activities. Any other location is less sustainable because it increases transport energy costs.

A building which can be used for many different purposes and is easily adapted to serve many different activities during its lifetime has a flexibility that reduces the need for demolition and rebuilding to serve changing needs (Bentley et al., 1985). Buildings are usually designed to meet the specific requirements of one particular owner or organization. This results in highly specialized buildings created by a designer for his or her clients. During the building design process, thought may be given to the current users and their needs, but very little to the general public and none at all to future generations. A building designed in this way to accommodate specialized activities is often difficult to adapt to changing needs. This is in marked contrast to the flexibility that is often a feature of traditional building design. Behind the ordered classical facades of the Georgian and Regency terrace is an interior which, despite the constraint of a load-bearing structure, has proved flexible enough to be adapted for offices or for multi-family occupation. Such flexibility in internal planning has been termed 'robustness'. A fine example of 'robust' design is Abercrombie Square, Liverpool, where three sides of the square's Georgian terraces have been converted for the use of The University of Liverpool (Figure 2.22). The green approach to urban design supports and fosters architectural solutions that exhibit the flexibility typical of the Georgian terrace - that is, building designs - which, because of their geometry and internal structural organization, are capable of a variety of uses.

Achieving a sustainable and flexible built form poses a great challenge to the designer: an examination of some of the traditional forms developed in the past, both in the temperate climatic zones and in the tropical regions of the world may present some useful ideas as a starting point in the search for an innovative but essentially simple urban architecture.

The first limitation imposed by a strict interpretation of the discipline of sustainability is a maximum building height normally of four stories: there may indeed be cases for exceeding this limit in the centres of some of our great cities, but generally speaking if sustainability is the aim, then four storeys is a reasonable maximum building height for most urban development. At this height, most activities — including residential — can be accommodated without the need for the able-bodied to use a lift. It

may, however, be necessary to organize the Figure 2.22 Abercrombie structure so that those with special needs are Square, Liverpool catered for on the ground or first floors. The width of a building in temperate climates should be determined by the conditions necessary to achieve good natural lighting in all main rooms. Since the best-lit areas in the building are within 4 metres of the external walls, the optimum width of the building is between 9 and 13 metres (Bentley et al.,

1985). A 9-metre-wide building permits the planning of two well-lit rooms on either side of a corridor, while a building greater than

13 metres wide with deep floors has an excessive amount of badly lit space in its middle section. A plan shape, 9 to 13 metres wide, is capable of a number of different arrangements, and so can accommodate different activities. Incidentally, plan shapes of these dimensions not only ensure good lighting conditions but can also be ventilated naturally.

A number of authors have suggested that the sustainable city is one where mixed land uses is the norm, as opposed to the

'modernist city' where urban functions were separated in the form of large zones of single use (Vale and Vale, 1991; Owens, 1991; The Urban Task Force, 1999). The vitality of the city can be enhanced further if a mix of activities occurs within buildings, in addition to those that occur at the scale of the neighbourhood or locality. The mixing of functions within buildings is likely to maintain activity in the streets at all times in the day. Buildings designed for a combination of, for example, flats and office space are more likely to be successful if the width of the block is about 10 metres; building blocks wider than 10 metres are unsuitable for double-aspect residential accommodation, which is the most flexible housing type in the British climate, where it is important for sunlight to reach all the main rooms. With the double-aspect home, most orientations are acceptable. One of the standard building blocks of the northern European city is, therefore, 9 to 13 metres wide and about four stories high: it has a traditional pitched roof to protect it from snow and rain, while at the same time providing an opportunity to insulate the building adequately. The three- to six-storey linear building block is found in many European cities: as the standard urban built form it serves the purpose well and is capable of many interpretations.

In contrast, other building forms have developed appropriate to conditions in tropical regions of the world. In the harsh climate of the humid tropics, conditions are such that good natural ventilation is critical. These conditions impose certain requirements on the plan form of a building and its cross-section: ideally, buildings should be one room wide and have an access veranda along one side with openings in both long facades to ensure cross-ventilation; this is essential if air-conditioning is to be avoided. In contrast again, the traditional building form in arid tropical regions is often deep with internal spaces that are lit and ventilated from secondary sources or from deep-shaded courtyards (Moughtin, 1985; Koenigsberger et al., 1973).

A key element in the design of green or flexible buildings, which are capable of modification for different activities, is the staircase and associated facilities. The staircase, landing and service ducts are usually grouped to serve a number of units on different floors. When a building changes use and is remodelled internally, these shared facilities - since they serve the same function for the new use - remain unchanged. Because this service element is so expensive to change during modification or refurbishment, it is often referred to as the 'hard zone'. 'Usually these spaces are 'hard', and.. .must be positioned where they will not restrict the use of the remaining space'. (Bentley et al., 1985). The optimum position for such hard zones is at intervals of 10 or 20 metres; at these intervals a variety of spaces can be arranged, including small or double-aspect office units and also larger floor areas of open office space. Such distributions of service core, or hard elements can also be used for residential purposes. For example, in buildings that have hard zones 10 metres apart it is possible to accommodate a single floor flat (apartment) of 50 square metres, a two-storey maisonette (duplex) of about 100 square metres, or a three-storey town house of 75 square metres.

The building envelope - that is, the external walls and roof together with the ground slab - is the part of the building where heat loss is registered. It is here also that the building must be made weatherproof in other ways. A building which has the lowest ratio for the area of the envelope to the usable floor area, not only costs less to build for any given building volume (assuming the same materials are used in the construction), but also uses less energy to construct and is more efficient in terms of energy use during its working lifetime. Energy costs - both the energy expended in the construction and in the running of the building - tend to increase as the ratio of the area of the building envelope to the usable floor area increases. A sustainable building is, therefore, one where its envelope is the smallest for a given usable floor area. The single-storey square plan has an advantage over the elongated rectangular plan shape, but two-, three- and four-storey buildings are more effective than both in terms of energy conservation.

The relationship of energy expenditure and building geometry has been considered so far for buildings standing in isolation as three-dimensional forms in space. In cities this is not always the case. It has been argued elsewhere, in this series of books on urban design, that the city comprises of spaces surrounded and formed by buildings (Moughtin, 2003). In terms of energy conservation there is much to commend this built form. By grouping small units together, the semi-detached house rather than two detached houses, or the terrace rather than semi-detached houses, it is possible to make savings in the area of external walling or envelope. Furthermore, if the plan shape of each unit is changed from a square to a rectangular one with a narrow building frontage, then additional savings in the area of the external wall can be made: there is then a corresponding conservation of energy. By composing the individual units into three-and four-storey blocks of flats or apartments, additional savings in the size of the building envelope is possible without the energy expense of providing lifts. This rather oversimplified argument presupposes that disadvantaged or special needs groups are allocated ground-floor accommodation.

Further energy savings can be made by designing the building to work well within the conditions set by the local climate. The vernacular tradition has much to teach in the art of relating the building to its site. The traditional dwelling in countries with colder climates is often sited just below the brow of a hill on a southward slope: it is protected from the cold northerly winds by the hill, which is often augmented with a shelterbelt of trees and bushes. The northern face of the building usually has few openings, and if it is a farmhouse it may be further protected from the weather by outhouses. The southern facade contains the main windows maximising the benefit of any sun. This common-sense approach to the location of a building on its site and the organization of the building elements to mitigate the worst effects of a cold winter climate has valuable lessons for the greening of building design. It would seem from this model that the ideal orientation for a building in our climate is with its long axis running east to west. The northern facade should be fronted by accommodation not requiring good views or good lighting, and by rooms where the highest levels of heating are not necessarily desirable - that is, this wall acts a barrier between the cold outside world and the snug interior living rooms. The type of accommodation facing north would be circulation space, storage, toilets and, possibly, working kitchens. In contrast, the rooms with a southern aspect would be the living rooms and bedrooms. Large windows are desirable in the southern face of the

Figure 2.23 The Orangery, Wollaton Hall, Nottingham

Figure 2.24 The Orangery, Wollaton Hall, Nottingham building to provide not only light but also passive solar heating.

Passive solar energy can provide up to 20 per cent of the annual space heating required for a well-insulated building, but it does have implications for the orientation of the building. For effective solar gain, window openings should be in walls with an orientation within 30 degrees east or west of south with a southern orientation being the optimum position. There are, however, problems with large south-facing windows in domestic buildings in this country where we place great emphasis on privacy: it is usual, particularly in residential areas, for frontages to face frontages. An arrangement where the front of one house overlooks a neighbour's backyard is generally unacceptable in 'Middle England'. A north-south orientation for the long axis of terrace housing is more suited to British conditions. With this orientation it is possible for the front of one house to face the front of the house opposite while both living rooms receive sunshine, one side in the afternoon and the other side in the morning. Large south-facing windows designed to generate solar heating, if overlooked, will be unacceptable to the occupant in this country and will be draped in net curtains to reestablish privacy, so defeating the original purpose. In buildings not dominated by the cultural need for privacy, such as schools, universities and offices, it may be possible to give greater priority to an orientation which maximizes the use of passive solar heating.

The conservatory - a common feature of many Victorian and Edwardian villas (Figures 2.23 and 2.24) - is becoming increasingly popular with home owners. It is a reasonably low cost and culturally acceptable method of passive solar heating in the home. It also forms a useful buffer between the external climate in winter and the interior of the building. The conservatory is most appropriately placed on the south, east or west walls. If not properly designed, the conservatory - even when well sited - can be a source of heat loss in the winter and cause overheating in the summer: adequate ventilation is essential, and the wall on which it is placed should be well insulated and fitted with double-glazed windows. Buildings designed specifically for use with a conservatory or sunspace offer great scope to create comfortable spaces, and energy saving. The conservatory also facilitates food production, its traditional role in the past. In addition, the sunspace or conservatory offers an opportunity for innovative design. The glass atrium and the street arcade are both features which, like the conservatory, modify the internal climate. They also enhance natural lighting within a building complex while being exciting visual additions to the urban realm (Figures 2.25-2.28).

It may appear from the previous paragraphs that the application of the principles of sustainable development will result in an urban form comprising a blanket of four-storey blocks arranged in serried ranks of parallel rows in order to maximize solar gain and energy efficiency. Energy efficiency in built form is, however, only one (albeit important) aspect of sustainable development. Other factors such as food production, landscape protection, maintaining biodiversity and energy-efficient movement of goods and people are also important considerations in the planning and design of the sustainable city. Each new addition to the city is designed for a specific site. The existing patterns of development condition the ways in which the principles of sustainability are applied. Additions to the city will be located along particular street lines and about specific neighbouring properties. It is this context, which sets the parameters for new development and to which the discipline of energy conservation must be applied. Even on greenfield sites, which in a sustainable city would be avoided if possible, the urban designer is not presented with a carte blanche. The urban designer cannot ignore contours, special

Figure 2.25 Leadenhall Market, London

Figure 2.26 Leadenhall Market, London

landscape features and local architectural form: these factors are the stimulus for the development of culturally acceptable solutions whereby the general principles of sustainable development can be applied for a site-specific purpose.

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